The purpose of water processing for water used during ultrasonic focusing tumour ablation treatment is to deaerate said water, i.e. to extract air solved therein out of said water, currently by means of water circulation vacuum deaeration, in which said water is circulated in a vacuum environment and the air solved in the water is separated out or deaerated thereby. Presently, the vacuum pumping unit in a water processing system for water used during ultrasonic focusing tumour ablation treatment uses a slide valve pump-Roots vacuum pump set or a water cycling vacuum pump-Roots vacuum pump set. The water circulation is made running by the water pump, since the slide valve pump is a kind of oil-seal vacuum pump and water is processed therein, the water undergoes vapourization and condensation, thus often there is water coming into the slide valve pump, causing contamination to the oil. The water cycling pump makes quite strong noise, and these two kinds of pumps have complicated structures and high costs. The water circulation in those water processing systems relies on their water pumps, which operate at very low efficiencies under vacuum environment, and of which the water outlet has to be put below water level otherwise the water will not come out. Even if the water outlet is put below water, the water pump can operate only when the water has been deaerated to some extent. And the water pump cannot maintain normal operation during the whole deaerating process, and putting the water outlet within the water does no good to the deaeration. Furthermore, the deaeration is not very effective by the single time deaerating using just a single water tank.